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Abstract extracted from page 1 of Report 263, Volume 1:

ABSTRACT A regional geochemical survey was conducted during 1988-89 by drilling Rotasonic cores of buried glacial drift over roughly 33 townships of Archean (Superior Province) terrane in southern Koochiching and northern Itasca counties between Big Falls and Bigfork. The objectives are directed at mineral potential evaluation and include the identification of glacial drift stratigraphy, favorable stratigraphy and sample media for geochemistry, examination of saprolite and bedrock lithology, and the organization of pertinent data into a computer database.

The underlying Archean bedrock (Quetico and Wawa subprovinces) is poorly understood, being largely unexplored prior to the current Minnesota Geological Survey (MGS) mapping program. Twenty-three Rotasonic drill holes, totaling 4,232 ft., were cored in 34 drilling days in the Effie area. The glacial drift stratigraphy logged by Gary Meyer (MGS) is more complex than to the east or north (Martin, et al., 1988). We have identified the late Wisconsinan Koochiching lobe and Rainy lobe drift, older (pre-late Wisconsinan) drift and saprolite. Lumping the stratigraphy into five general packages--Koochiching drift, Rainy drift, Old Rainy drift, Winnipeg drift, and laterite--there were 14 different stratigraphic columns found in the 23 drill holes. Twelve holes encountered saprolite, ranging in thickness from 1 to 58 feet.

Project Area

Twenty holes reached bedrock and/or saprolite. The average total depth was 185 feet, ranging from 60 to 296 feet deep. The bedrock data is being integrated into the broader-scale MGS mapping program (Jirsa, 1989A). In a cooperative effort, the Minerals Division (DNR) drilled 9 of the 23 holes at locations the MGS had selected for their current geologic drilling and mapping program in this area.

The glacial drift and saprolite core samples were split and composited within stratigraphic units for processing of heavy mineral concentrates (HMC), -63 micron fraction for Au & Ag, and clay size fraction for base metals. Roughly 190 HMC samples and 190 complementary -63 um samples were analyzed for gold. Limited mineralogy work has been done on the saprolite and nonmag HMC samples. The complexity of the stratigraphy automatically limits our ability to make generalizations about the trace element distributions by subdividing the total sample number into many small sUbpopulations.

Good cores of older tills and saprolites were obtained for the first time and are available for inspection. Significant information relating to identification of drift types and sample media has been compiled. The average number of gold grains per 10 kg of till samples is much higher here than to the east. Summarizing the HMC results, there are 4 holes with multiple-sample gold grain counts worthy of further evaluation, and 4 other holes with other multielement values greater than or equal to 3 times the median. None of the patterns are interpreted to be adjacent to a bedrock source. The limited dataset does not offer good insights into the geochemical variability expected at the local or property scale. Therefore, the significance of the elevated values in the above 8 drill holes is very I difficult to rate.

Rotasonic cores were drilled in three additional townships (T46N-R29W, T46N-R28W, T45NR27W) in east-central Minnesota overlying Early Proterozoic bedrock. The stratigraphic and geochemical data obtained will be used to plan for possible future mineral evaluation surveys in that region.

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3. Digital data available:

The zip file contains data for samples extracted from twenty seven drill holes described in the Minnesota Department of Natural Resources (MnDNR), Division of Land and Minerals Report “Regional Geochemical Survey of Glacial Drift Drill Samples Over Archean Granite - Greenstone Terrane in the Effie Area, Northern Minnesota - Report 263,” published 1989. Each folder contains all of the data from the report in a different format. The data is presented in a Microsoft Access database, Microsoft Excel 97-2003 workbooks, dBase IV files, and ArcGIS shapefiles. The conversion of the original ASCII digital data to these formats was completed in September of 2012. The sixteen data sets enumerating drill hole or core sample data contain geospatial information in the form of Universal Transverse Mercator (UTM) East and North coordinates, a “Z” field with the elevation of the drill hole top, and elevation the of top and bottom of the individual samples; all elevations are in feet above sea level. A new field named “Sample_Num,” concatenating the “Sample” and “Sample_Typ” fields, has been added to tables with a “Sample” field in order to facilitate table joins. Detailed descriptions of the other data fields can be found in Part I and Part II of the report listed above. The data is designed to be used as a supplement to the report and plates.

For more information:

Dennis Martin
500 Lafayette Road
St. Paul, Minnesota 55155-4045
tel. (651) 259-5405
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